1. Field of the Invention
This invention relates to improvements in an internal combustion engine of the split type, operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
In general, internal combustion engines demonstrate higher efficiency and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed which have active cylinders which are always active and inactive cylinders which are inactivated when the engine load goes below a given value. Such split engines usually have an intake passage divided into first and second branches, the first branch being associated with the active cylinders and the second branch being associated with the inactive cylinders. The intake passage is usually provided with a stop valve. Such split engine operating system may be responsive to an engine load drop below a given value to close the stop valve so as to cut off the flow of air to the inactive cylinders and also to cut off the flow of fuel to the inactive cylinders while increasing the amount of fuel and air to the active cylinders when operating in a split engine mode where the engine operates only on the active cylinders. This increases the active cylinder loads in a split type engine, resulting in higher fuel economy.
One difficulty with such split type internal combustion engines is that a large change occurs in air/fuel ratio, resulting in an increase in exhaust emissions and a reduction in fuel economy when engine operation is shifted between its full engine and split engine modes. The reason for this is that the amount of fuel supplied to the cylinders is generally doubled or reduced to half as the engine load goes below or above a given value while the stop valve closes or opens with a delay due to friction and air resistance.